Master of Science (MS)



Document Type



Reaches to remembered target locations often result in different endpoint precision when compared to reaches to actual (seen) targets. Interestingly, errors are observed whether the reach to the remembered location is performed in an environment with or without allocentric cues (visual cues from the environment) available. People tend to point below remembered target locations in the dark relative to normal room lighting while seated, standing, and reaching with a step. In this study we questioned the effect of gravitational influences on upper extremity reaching and pointing accuracy in dark and illuminated environments. We hypothesized that alterations in body orientation would alter endpoint reaches to final remembered target locations differently for the two visual conditions. Young healthy adults were asked to produce reaching movement in SUPINE and UPRIGHT body orientations or straight arm pointing movements in UPRIGHT and INVERTED body orientations to real and remembered target locations. Three targets directly in front of the midline were presented at shoulder level and shoulder level ±30 cm. Prior to movement participants anchored their gaze on the displayed target before pointing to its real or remembered location. Targets in remembered trials were removed or covered before pointing in normal room lighting (LIGHT) or complete darkness (DARK). At least 6 trials were performed to each target in each body orientation, starting arm position, and visual condition. Endpoint errors, displacement, peak velocity, and movement time were calculated for each participant and compared across target level, body orientation, and visual condition for each starting arm position using repeated measures ANOVAs. In the DARK participants often produced errors corresponding to less displacement and the undershooting of remembered target locations as compared to LIGHT and REAL visual conditions. Control of smaller movement amplitudes observed in darkness primarily with greater movement excursions occurred regardless of muscle activation or body orientation. The present study revealed that the effects of the gravitational pull for endpoint precision in darkness are minimal at best, thus cannot explain the differences in endpoint accuracy between visual conditions.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Hondzinski, Jan

Included in

Kinesiology Commons